Conventional devices for producing interferograms have one or more moving parts, such as a mirror or other reflective element, and accumulate data from several measurements of electromagnetic radiation at a succession of different mirror positions. These devices are usually variants of the Michelson interferometer design, and the interferograms are recorded for a number of different positions of the moving mirror and analyzed for spectral content. The distance between mirror positions can be very small. For example, optical interferometry mirror movements can be 1 millionth of a meter or less. A high precision mechanism is therefore required to reposition the mirror and maintain its reflective surface in a plane that is normal to the direction of propagation of the sample input beam. Although construction of a Michelson-type interferometer is a major optomechanical challenge and good instruments can be quite expensive, the Michelson interferometer remains the most widely used instrument of its kind, and over the years, many variations have been designed. In particular, substantial effort has been devoted to the design of staging platforms, actuators, transducers, drive mechanisms, and the like, to improve positioning and control of the moving mirror.
Michelson-type interferometers are subject to misalignment and distortion from vibration, shock and environmental changes and must be field hardened for use outside a laboratory environment. For example, the Michelson-type interferometer in the Army's M21 Automatic Chemical Agent Alarm is housed in an elaborate and costly vibration isolating, climate controlled enclosure. Michelson-type interferometers may also experience problems in applications where the input signal changes rapidly during the time the mirror takes to travel the distance needed for acquiring a complete interferogram. For example, an interferometer that is operating from a fast moving platform such as an airplane with a given field-of-view (FOV) can experience an input signal that changes more rapidly than the acquisition time of a complete interferogram. In this case, the “scene” or region of space being sampled within the instrument's FOV is not constant over the acquisition time, and the interferogram is thus composed of a mixture of data from several different scenes.
These and other problems are solved, at least in part, by embodiments of a single-exposure, no moving parts interferometer in accordance with the present invention.